1. Field of the Invention
The present invention relates to an optical fiber connecting body in which a positive dispersion fiber having chromatic dispersion at a transmission wavelength is connected to a dispersion compensating fiber for canceling the chromatic dispersion of the positive dispersion fiber.
2. Description of the Prior Art
An optical fiber generally arranged as an optical communication transmission path at present is a single mode optical fiber having zero dispersion in 1.3 .mu.m band.
It is now considered at present to perform high speed communication by optical signal having 1.55 .mu.m in band so as to increase the capacity of an optical communication network with respect to this single mode optical fiber already arranged.
This single mode optical fiber having zero dispersion wavelength in 1.3 .mu.m band has about 17 ps/nm/km in chromatic dispersion around 1.55 .mu.m. Therefore, a dispersion compensating means for compensating this chromatic dispersion is required when optical signal having 1.55 .mu.m in band is used.
There is a method for canceling this dispersion by connecting a dispersion compensating optical fiber having negative dispersion in an optical fiber transmission path as a practical method of the dispersion compensating. However, the dispersion compensating optical fiber used for this purpose has a considerable long length. Accordingly, it is actual to wind this dispersion compensating optical fiber in a coil shape and assemble this optical fiber into the optical communication transmission path as a package.
It is convenient in treatment to make the dispersion compensating optical fiber compact so as to assemble such a long dispersion compensating optical fiber into a transmission device as a package.
However, when the long dispersion compensating optical fiber is wound in a coil shape, an occupying size of the coil depends on a volume and a vacant space ratio of the optical fiber. Therefore, when the long dispersion compensating optical fiber has a large cross section, i.e., a large diameter, this dispersion compensating optical fiber becomes a large coil, which leads to an increase in size of the transmission device which contains the dispersion compensating optical fiber.
Therefore, it is normally desirable to reduce an outside diameter of the dispersion compensating optical fiber as much as possible.
Fusion splicing is generally used when the dispersion compensating optical fiber is connected to the normally used single mode optical fiber of zero dispersion having 1.3 .mu.m in band. However, the normal single mode optical fiber has core diameter of 10 .mu.m. In contrast to this, the dispersion compensating optical fiber has core diameter of 2 .mu.m. Accordingly, the core diameters of the single mode optical fiber and the dispersion compensating optical fiber are different from each other. Further, when the outside diameter (cladding diameter) of the dispersion compensating optical fiber is reduced in comparison with the normal single mode optical fiber to reduce the diameter of the dispersion compensating optical fiber, a problem exists in that it is more difficult to connect these optical fibers to each other since the dispersion compensating optical fiber is connected to the single mode optical fiber having a normal outside diameter. And in that a connection loss is increased.